Image processing apparatus and image processing method for correcting distortion in photographed image

An image processing method executed by an image processing apparatus including an image photographing unit and a control unit, the image processing method comprising:

• a document image acquiring step of acquiring a document image including at least an image of a document photographed by the image photographing unit;
• a contour extracting step of extracting, based on luminance of the document image, a contour of the document from the document image acquired at the document image acquiring step;
• a distortion position detecting step of detecting a contour straight line located at a location where a distance between the contour extracted at the contour extracting step and a center point of a rectangle having the minimum area surrounding the contour is shortest, the contour straight line being detected as a distortion position of a distortion in the document image, the contour straight line being located on the contour, the distance being on a diagonal line of the rectangle;
• and
• a corrected image generating step of performing a geometric correction on the document image to extend the contour to a correction reference line determined from the distortion position detected at the distortion position detecting step, and generating a corrected image having the distortion in the document image corrected, wherein
• the steps are executed by the control unit.